Question

s${}_1$ and s${}_2$ are two sound sources of frequencies 338 Hz and 342 Hz respectively placed at a large distance apart. The velocity with which an observer should move from s${}_2$ to s${}_1$ so that we may hear no beats will be: (velocity of sound in air = 350 m/s)

• A. 1 m/s
• B. 2 m/s
• C. 3 m/s
• D. 4 m/s

Answer 1

Answer: (B)

2 m/s

Frequency when observer is moving away $=\left(\frac{v-v_0}{v}\right)f$

Frequency when observer is moving towards $=\left(\frac{v-v_0}{v}\right)f$

$\left(\frac{v-v_0}{v}\right)338=\left(\frac{v-v_0}{v}\right)342$

$4v=680v_0$

$v_0=\frac{4\times 330}{680}=2m{s}^{-1}$